Uncooled micro-bolometers based thermal focal plane array (UC-FPA) opening new opportunities for IR detection are disclosed in [1]. The US-FPA is characterized by small size, lower power consumption and a reduced price. As a result, the US-FPA-based cameras find use in many military and commercial applications as thermal imaging devices [2]. Portability of UC-FPA allows mounting the US-FPA-based cameras on micro unmanned air vehicle, which is very attractive for agricultural and environmental monitoring.
Radiometric mapping of crops is disclosed in [3]. Although the camera was mounted with a protective shield, FPA temperature was influenced by wind velocity and to some extent by change in radiation level related to clouds cover. Convection from a surface depends on fluid velocity [4]. Thus, changes in FPA temperature may be explained by variable wind velocity around the camera, where the envelope temperature affects the FPA temperature [2]. Surface temperature also depends on heat exchange by radiation balance with the environment [4]. The drift in the FPA temperature limits the possibility to gain a radiometric image from the thermal camera. Thus calibrating the camera response to stabilize the camera readout is an important challenge.
A typical micro-bolometer comprises two main parts: an absorber heated by thermal radiation and a thermometer the resistance of which changes with temperature. The micro-bolometer readout (r(x,y)) is in voltage or current values [1]. The obtained readout is translated into a gray level signal. Isolation of the micro-bolometer thermally allows thermal sensing without the burden of expensive cooling.
Thus, there a long-felt and unmet need to provide a US-FPA-based camera configured for obtaining radiometric images by calibrating thermal images.